A metal skeleton SiC ceramic auxiliary heating device for microwave sintering

Abstract

The present invention belongs to the field of high-temperature microwave heating, and specifically relates to a metal skeleton SiC ceramic auxiliary heating device for microwave sintering. It includes a stainless steel bearing box, a mullite fiber box, a crucible, alumina asbestos and a SiC support plate with an embedded metal skeleton; alumina asbestos is filled between the mullite fiber box and the crucible arranged in the stainless steel bearing box, a SiC support plate is placed in the crucible, and the sample is placed on the SiC support plate during heating. The metal skeleton SiC ceramic support plate of this device is in direct contact with the heated sample and plays a key role in the entire heating process. It can not only assist in heating the heated sample, but also keep the heated sample warm, thereby reducing the heat loss of the heated sample, and can homogenize the sample temperature, and finally improve the heating efficiency of the heated sample. The auxiliary heating device has a simple and reasonable structure, and the metal skeleton SiC ceramic support plate is easy to manufacture, which can greatly improve production efficiency.

Description

Technical Field

[0001] The invention belongs to the field of high-temperature microwave heating, and in particular relates to a metal skeleton SiC ceramic auxiliary heating device for microwave sintering. Background Art

[0002] At present, the commonly used high-temperature sintering preparation methods for ceramics, metal compounds, non-metallic compounds and organics are conventional sintering methods and microwave sintering methods. Among them, the heat of the conventional sintering method is transferred from the surface of the object to the inside by heat conduction. There is usually a large temperature gradient inside the object, and the heating is slow and the heating time is long, which easily causes a lot of energy waste. Microwave sintering is an efficient heating method that uses the dielectric loss of the material to generate heat so that the material can be heated from the inside to the outside. It can achieve the overall heating of the material. Therefore, the material heats up quickly, the internal temperature gradient is small, and the heating is uniform, so that the properties of the sintered material are uniform, with the advantages of fine grains and good density. In addition, microwave sintering also has the characteristics of high efficiency, energy saving, and cleanliness, and can achieve structures and performance that cannot be achieved by conventional sintering methods. However, the sintering temperature of some materials (such as ceramic materials) is high, and the relative dielectric constant is small in the low temperature stage, and the wave absorption performance is poor, resulting in a slow heating rate in the low temperature stage. Therefore, the design of the auxiliary heating device is one of the important factors that currently limit the application and development of microwave sintering technology. Reasonable design of the auxiliary heating device can improve the heating efficiency of the heated material.

[0003] The common auxiliary heating device for microwave sintering disclosed at present is to sinter by burying powder to assist heat, and fill some other insulation materials in the mullite fiber box, such as a heat preservation and auxiliary heating device for microwave sintering ceramic tool materials published in the patent application publication number (CN105091604A). The device includes an outer mullite box, a heat preservation zone composed of high-temperature resistant alumina fiber cotton and high-temperature resistant alumina foam bricks, and an auxiliary heating zone composed of silicon carbide, graphite and activated carbon powder. The device can withstand a sintering temperature of nearly 2000°C during the sintering process, and has excellent insulation effect. However, in this patent, the alumina fiber cotton is in direct contact with the crucible, which will cause the temperature of the crucible to dissipate too quickly. And there is only one preparation cavity, and the preparation efficiency of the tool material is low. In the patent application publication number (CN 106288785 A), a polycrystalline mullite fiber cotton layer is arranged around the crucible, so that the temperature inside the crucible is uniform and the temperature is not easy to dissipate, which ultimately makes the heating rate of the ceramic tool material faster and the temperature field more uniform. A multi-cavity microwave sintering and heat preservation device with more than three sintering cavities is used, which can prepare multiple and various ceramic tool materials at one time, thereby increasing the preparation efficiency to a certain extent; however, this method adopts the buried powder sintering method, which also has the following problems.

[0004] In the above-mentioned schemes, the design and optimization of the insulation material outside the crucible are mainly carried out, and it is not considered that when the silicon carbide powder is buried to assist in sintering, although the ceramic material can be assisted in heating at a low temperature stage, so that it can heat up quickly, when the temperature gradually increases and reaches the high temperature stage, the conductivity of the silicon carbide material increases, which will shield the electric field around the heated sample, thereby affecting the heating of the heated sample and ultimately reducing the heating efficiency of the heated sample. In addition, these patents can only perform microwave sintering of a small number of samples and small-volume samples, and cannot sinter batch samples and large-volume samples, resulting in low efficiency in the preparation of ceramic materials. Summary of the invention

[0005] The object of the present invention is to provide an auxiliary heating device which is resistant to high temperatures and can improve the heating efficiency of batch samples and large-volume samples.

[0006] The technical solution to achieve the purpose of the present invention is: a metal skeleton SiC ceramic auxiliary heating device for microwave sintering, comprising a stainless steel bearing box, a mullite fiber box, a crucible, alumina asbestos and a SiC sintering plate with an embedded metal skeleton;

[0007] Alumina asbestos is filled between the mullite fiber box and the crucible in the stainless steel bearing box, and a SiC setter plate is placed in the crucible. During heating, the sample is placed on the SiC setter plate.

[0008] Further, the mullite fiber box includes a mullite fiber box cover, a mullite fiber box base and a mullite fiber box body;

[0009] A cylindrical temperature measuring hole is provided at the center of the mullite fiber box cover.

[0010] Furthermore, the crucible is a boron nitride ceramic crucible, and the crucible comprises a crucible box and a crucible cover plate;

[0011] A protrusion is provided on the upper surface of the crucible cover plate, and a cylindrical through hole is provided inside the protrusion and on the corresponding crucible cover plate. The axis of the cylindrical through hole is the same as the inner diameter of the cylindrical temperature measuring hole and the axis coincides. An annular step groove is provided on the surface of the crucible cover plate that matches the side wall of the crucible box, and the width of the step groove is the same as the thickness of the side wall of the crucible box.

[0012] Furthermore, the inner diameter of the cylindrical through hole is 30±5 mm, and the height of the cylindrical through hole is 35±5 mm.

[0013] Furthermore, the dimensions of the SiC support plate are 208±20mm in length, 130±15mm in width, and 15-20mm in height; the metal skeleton in the SiC support plate is arranged in multiple rows and columns, and is composed of multiple rows and columns of metal rods, the spacing between adjacent metal rods in each row or column is 10-20mm, and the length of the metal rod is 100-120mm.

[0014] Furthermore, the material of the metal skeleton is selected from high conductivity, high melting point metal, which has a reflective effect on electromagnetic waves, can change the electromagnetic field distribution, and enhance the electromagnetic field intensity on the heated sample, thereby improving the heating efficiency of the heated sample.

[0015] Furthermore, the material of the metal skeleton is copper, iron or platinum.

[0016] Furthermore, the mullite fiber box cover and the mullite fiber box base are rectangular, the mullite fiber box body is a square box body; and the boron nitride ceramic crucible is a rectangular box body.

[0017] Furthermore, a space is reserved inside the boron nitride ceramic crucible to facilitate the placement of metal skeleton SiC support plates and heating samples of different shapes and sizes.

[0018] Furthermore, the alumina asbestos can withstand temperatures above 1700°C, the mullite fiber box cover, the mullite fiber box body and the mullite fiber box base can withstand temperatures above 1700°C; the boron nitride ceramic crucible is made of hexagonal boron nitride and can withstand temperatures up to 3000°C in a nitrogen atmosphere.

[0019] Compared with the prior art, the present invention has the following significant advantages:

[0020] (1) The present application uses a support plate. First, since some heated sample materials have poor microwave absorption ability at low temperature, the support plate quickly absorbs microwaves and heats up, so that the sample quickly reaches the temperature of self-heating, thereby improving the heating rate of the heated sample. Second, compared with powder sintering, at high temperature, there will be no shielding of the electric field, thereby reducing the heating efficiency. That is, the use of a support plate to assist heating is conducive to improving the heating efficiency of the heated sample;

[0021] (2) The present application adds a metal skeleton with high electrical conductivity and high melting point to the setter plate. The metal material is added to the SiC setter plate. Firstly, it can prevent the metal material from being placed in the air and "sparking" under high temperature, thereby avoiding the occurrence of danger. Secondly, due to the high electrical conductivity of the metal material, it reflects electromagnetic waves. When arranged in the SiC setter plate, it will change the electromagnetic field distribution on the SiC setter plate and the heated sample, enhance the electromagnetic field intensity on the SiC setter plate and the heated sample, thereby further improving the heating efficiency of the heated sample and improving the temperature uniformity of the heated sample to a certain extent. At the same time, because high-temperature heating is required, it is necessary to select a high-melting-point metal, such as copper, iron, platinum, etc.

[0022] (3) The boron nitride ceramic crucible of the present application is designed with a rectangular structure and a certain space, so that the shape and size of the metal skeleton SiC ceramic support plate and the heated sample placed inside are not fixed, and batch samples and large-volume samples can be sintered, avoiding the problem of frequent replacement of the boron nitride ceramic crucible; at the same time, the upper side surface of the cylindrical vertical through hole above the crucible adopts a stepped shape, which can effectively prevent the volatiles from volatilizing into the box during the sample heating process and damaging the auxiliary heating device;

[0023] (4) The device has a simple and reasonable structure, the metal skeleton SiC ceramic support plate is easy to manufacture and disassemble, and the internal components are easy to replace, which can greatly improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of the metal skeleton SiC ceramic auxiliary heating device for sintering of the present invention.

[0025] Figure 2 It is a three-dimensional schematic diagram of the metal skeleton SiC ceramic auxiliary heating device for sintering of the present invention.

[0026] Figure 3 It is a three-dimensional schematic diagram of the metal skeleton SiC ceramic support plate of the present invention.

[0027] Figure 4 This is the temperature distribution cloud diagram of batch samples heated by microwave when only SiC support plate is used.

[0028] Figure 5 This is the electric field distribution cloud diagram of batch samples heated by microwave when only SiC support plate is used.

[0029] Figure 6 Temperature distribution cloud diagram of batch samples heated by microwave when the metal skeleton SiC ceramic support plate is used.

[0030] Figure 7 Electric field distribution cloud diagram of batch samples heated by microwave when the metal skeleton SiC ceramic support plate is used.

[0031] Figure 8 This is the temperature distribution cloud diagram of large volume sample microwave heating when only SiC support plate is used.

[0032] Fig. 9 Temperature distribution cloud diagram of large volume sample heated by microwave when the metal skeleton SiC ceramic support plate is used.

[0033] Description of reference numerals:

[0034] 1-mullite fiber box cover, 2-temperature measuring hole, 3-cylindrical through hole, 4-alumina asbestos, 5-crucible cover, 6-crucible box, 7-heating sample, 8-SiC support plate, 9-metal skeleton, 10-mullite fiber box body, 11-mullite fiber box base, 12-stainless steel load-bearing box. DETAILED DESCRIPTION

[0035] The core of the present invention is to provide a metal skeleton SiC ceramic auxiliary heating device for microwave sintering, which can improve the heating efficiency of batch samples or large-volume samples.

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0037] like Figure 1-3 A metal skeleton SiC ceramic auxiliary heating device for microwave sintering includes a mullite fiber box cover 1, a temperature measuring hole 2, a cylindrical through hole 3, an alumina asbestos 4, a crucible cover 5, a crucible box 6, a heating sample 7, a SiC support plate 8, a metal skeleton 9, a mullite fiber box body 10, a mullite fiber box base 11, and a stainless steel load-bearing box 12.

[0038] In the device, the mullite fiber box cover plate 1, the mullite fiber box base 11 and the mullite fiber box body 10 constitute a mullite fiber box, and the outer side of the mullite fiber box is a stainless steel load-bearing box 12 for placement and fixing.

[0039] The boron nitride ceramic crucible is located at the center of the mullite fiber box, alumina asbestos 4 is filled between the boron nitride ceramic crucible and the mullite fiber box, and a circular temperature measuring hole 2 is provided at the center of the mullite fiber box cover plate 1.

[0040] The boron nitride ceramic crucible comprises a crucible box 5 and a crucible cover plate 6. A metal skeleton SiC ceramic sintering plate is placed inside the crucible box, and a heated sample 7 is placed on the metal skeleton SiC ceramic sintering plate.

[0041] A cylindrical through hole 3 is provided at the center of the crucible cover plate 5. The inner diameter of the upper part of the cylindrical through hole 3 is the same as the inner diameter of the temperature measuring hole and the central axis coincides with that of the temperature measuring hole. The upper surface of the cylindrical through hole 3 contacts the lower surface of the mullite fiber box cover plate 1.

[0042] The mullite fiber box cover plate 1 and the mullite fiber box base 11 are rectangular; the mullite fiber box body 10 is a square box body.

[0043] The alumina asbestos 4 can withstand temperatures above 1700°C, and the mullite fiber box cover 1, the mullite fiber box body 10 and the mullite fiber box base 11 can withstand temperatures above 1700°C.

[0044] The boron nitride ceramic crucible is a rectangular box. The upper surface of the cylindrical through hole on the crucible cover plate 5 is provided with an annular step groove, and the lower surface of the cover edge of the crucible cover plate 5 is also provided with an annular step groove, and the width of the step groove is the same as the wall thickness of the crucible body. The boron nitride ceramic crucible is made of hexagonal boron nitride and can withstand temperatures of up to 3000°C in a nitrogen atmosphere.

[0045] The dimensions of the cylindrical through hole 3 are as follows: the inner diameter of the cylindrical through hole 3 is 30±5 mm, and the height of the cylindrical through hole 3 is 35±5 mm.

[0046] A certain amount of space is reserved inside the boron nitride ceramic crucible to facilitate the placement of metal skeleton SiC ceramic support plates and heating samples 7 of different shapes and sizes.

[0047] The metal skeleton SiC ceramic setter plate has a main body of a SiC setter plate 8, with a metal skeleton 9 added inside to play the role of auxiliary heating, heat preservation and homogenizing the temperature field of the sample.

[0048] The metal skeleton 9 is made of a metal with high electrical conductivity and high melting point (such as copper, iron, platinum, etc.), which has a reflective effect on electromagnetic waves, can change the electromagnetic field distribution, and enhance the electromagnetic field intensity on the heated sample, thereby improving the heating efficiency of the heated sample. The metal skeleton 9 in the SiC support plate 8 is arranged in five rows and five columns, with an overall spacing of 10-20 mm and a length of 100-120 mm.

[0049] Since some materials have poor microwave absorption ability at low temperatures, by adding a setter, the setter transfers the temperature to the heated sample through its heat conduction, so that the heated sample can quickly reach the temperature of self-heating, thereby improving the heating efficiency of the heated sample. Furthermore, since metal materials have a reflective effect on electromagnetic waves, metal materials are added to the SiC setter to form a metal skeleton SiC ceramic setter. Since metal materials reflect electromagnetic waves, they will change the electromagnetic field distribution on the setter and the heated sample, and enhance the electromagnetic field intensity on the setter and the heated sample, thereby further improving the heating efficiency of the heated sample on the basis of having a setter.

[0050] In summary, the metal skeleton SiC ceramic support plate provided by the present invention can improve the electromagnetic field intensity on the SiC support plate and the heated sample, thereby improving the heating efficiency of batch samples or large-volume samples.

[0051] The simulated cloud diagrams of batch samples and large-volume samples are used to illustrate the improvement of the heating efficiency of the samples by the metal skeleton SiC ceramic support plate. Figure 4The figure shows the microwave heating temperature cloud diagram of the batch sample when there is only a SiC setter. From the figure, it can be seen that the temperature distribution of the sample located in the middle of the setter is roughly between 1750-1760℃, while the temperature of the sample located in the upper left corner and lower right corner of the setter is relatively high, reaching a maximum of 1801℃. The overall temperature difference of the batch sample is 50℃, and the overall average temperature is 1763℃.

[0052] Figure 5 The figure shows the electric field cloud diagram of the batch sample when there is only a SiC support plate. It can be seen that the electric field intensity distribution of the heated sample and the temperature distribution of the heated sample are highly consistent. The sample temperature is high where the electric field intensity is large, and the sample temperature is low where the electric field intensity is low. This is because the dielectric loss of the sample in the area with a large electric field is large, and the sample heating rate is fast. The dielectric loss of the sample in the area with a small electric field is small, and the sample heating rate is slow. Therefore, by enhancing the electric field intensity on the heated sample, the overall heating rate of the heated sample can be increased, thereby improving the heating efficiency of the batch heated sample. However, it can be found that the electric field intensity on the heated sample varies greatly, but the overall temperature difference of the heated sample is not large. This is because the support plate transfers heat through heat conduction, thereby reducing the temperature difference of the heated sample. Therefore, for batch heated samples, the support plate has a certain effect of homogenizing the temperature field.

[0053] Figure 6 The microwave heating temperature cloud diagram of batch samples on the metal skeleton SiC ceramic setter is shown. It can be seen from the figure that the temperature of the sample located in the middle of the setter is relatively improved compared with the whole, the temperature of the sample located in the upper left corner and the lower right corner is relatively high, and the temperature of the sample in the lower left corner and the upper right corner is relatively low. The overall temperature difference of the batch samples reaches 60℃, and the overall average temperature reaches 2126℃, which is 20.5% higher than that of the SiC setter alone. This is mainly because the added metal material reflects the electromagnetic field, thereby enhancing the electric field strength on the heated sample and improving the heating efficiency of the batch heated samples.

[0054] like Figure 7 As shown in the figure, compared with adding only SiC ceramic setter plate, the maximum and minimum values ​​of the electric field intensity have been improved to a certain extent, especially the minimum value has been improved by a large margin. In addition, due to the reflection of electromagnetic waves by metal materials, the electric field distribution on the heated sample is affected, thereby changing the temperature field of the heated sample, so that the temperature of the sample in the middle part has been increased to a certain extent.

[0055] Likewise, if Figure 8 The figure shows the microwave heating temperature cloud diagram of a large volume sample with only a SiC support plate. It can be seen from the figure that the average temperature of the entire sample is 1737°C. Fig. 9 The figure shows the microwave heating temperature cloud diagram of a large volume sample with a metal skeleton SiC ceramic setter. It can be seen from the figure that the average temperature of the entire sample is 2656℃, which is 52% higher than the heating efficiency when there is only a SiC setter. It can be seen that the use of an auxiliary heating device with a metal skeleton SiC ceramic setter for microwave sintering can improve the heating efficiency of the heated sample to a certain extent.

Claims

1. A metal skeleton SiC ceramic auxiliary heating device for microwave sintering, characterized in that: It comprises a stainless steel bearing box (12), a mullite fiber box, a crucible, alumina asbestos (4) and a SiC support plate (8) with an embedded metal skeleton (9); Alumina asbestos (4) is filled between the mullite fiber box and the crucible in the stainless steel bearing box (12), a SiC setter plate (8) is placed in the crucible, and the sample is placed on the SiC setter plate (8) during heating; The mullite fiber box comprises a mullite fiber box cover plate (1), a mullite fiber box base (11) and a mullite fiber box body (10); A cylindrical temperature measuring hole (2) is provided at the center of the mullite fiber box cover; The crucible is a boron nitride ceramic crucible, and the crucible comprises a crucible box (6) and a crucible cover plate (5); A protrusion is provided on the upper surface of the crucible cover plate (5), a cylindrical through hole (3) is provided inside the protrusion and on the corresponding crucible cover plate, the axis of the cylindrical through hole (3) is the same as the inner diameter of the cylindrical temperature measuring hole (2) and the axis coincides, and an annular stepped groove is provided on the surface of the crucible cover plate (5) matching the side wall of the crucible box, and the width of the stepped groove is the same as the thickness of the side wall of the crucible box; The dimensions of the SiC support plate (8) are 208±20 mm in length, 130±15 mm in width, and 15-20 mm in height; the metal frame (9) in the SiC support plate (8) is arranged in multiple rows and columns, and is composed of multiple rows and columns of metal rods, the spacing between adjacent metal rods in each row or column is 10-20 mm, and the length of the metal rod is 100-120 mm; The material of the metal skeleton (9) is a metal with high electrical conductivity and high melting point, which has a reflective effect on electromagnetic waves, can change the electromagnetic field distribution, and enhance the electromagnetic field intensity on the heated sample, thereby improving the heating efficiency of the heated sample.

2. The device according to claim 1, characterized in that The inner diameter of the cylindrical through hole is 30±5 mm, and the height of the cylindrical through hole is 35±5 mm.

3. The device according to claim 2, characterized in that The material of the metal skeleton (9) is copper, iron or platinum.

4. The device according to claim 3, characterized in that The mullite fiber box cover plate (1) and the mullite fiber box base (11) are rectangular, the mullite fiber box body (10) is a square box body; and the boron nitride ceramic crucible is a rectangular box body.

5. The device according to claim 4, characterized in that The boron nitride ceramic crucible has space inside, which is convenient for placing metal skeleton SiC sintering plates (8) and heating samples (7) of different shapes and sizes.

6. The device according to claim 5, characterized in that The alumina asbestos (4) can withstand a temperature of more than 1700°C, and the mullite fiber box cover (1), the mullite fiber box body (10) and the mullite fiber box base (11) can withstand a temperature of more than 1700°C; the boron nitride ceramic crucible is made of hexagonal boron nitride and can withstand a temperature of up to 3000°C in a nitrogen atmosphere.

Images